1. Field of the Invention
The present invention relates to a bonding method of a semiconductor device and a MEMS device package. More particularly, the present invention relates to a side-bonding method of a flip-chip semiconductor device for firmly bonding sides of the device, and a MEMS device package and a package method using the same.
2. Background of the Invention
The development of the package technology of bonding integrated devices is of considerable importance in miniaturization and high-performance of electronic goods. Therefore, the successful manufacturing of a micro-electromechanical system (MEMS) device depends heavily on package technology, and particularly, wafer level package technology is of great importance in the mass production of MEMS devices.
Packaging of a MEMS device is essential for protecting the device in view of the device properties, even if the MEMS device itself has excellent size and performance properties. In the case of a wafer level package, with the exception of adhesive bonding, etc., two substrates to be bonded should be spaced apart by less than 0.1 μm, which may be a limitation in developing devices. In addition, bonding through a specific chemical reaction is highly affected by the conditions externally applied for the reaction, such as temperature, voltage, material property and the like, which results in a great impact on the device manufacturing processes.
The bonding method for a conventional MEMS device package includes anodic bonding, silicon direct bonding, eutectic bonding, adhesive bonding, and the like.
FIG. 1 illustrates a schematic sectional view to show an example of anodic bonding. As shown in the FIG. 1, electrodes 30 and 40 are connected with upper and lower substrates 10, 10,′ which are formed by depositing a silicon film or oxide film on a specific glass good. Thereafter, a voltage of 100 V or more is applied thereto to form an oxide film on the interface to achieve bonding. However, such a bonding method only works for a specific material having a glassy contact interface. Therefore, bonding may not be achieved depending on the roughness of the wafer surface by which a bonding yield is greatly affected by particles. In addition, because the bonding method requires 100 V or more to be applied to the device, device failures may occur on the MEMS device during the bonding. Furthermore, the bonding method requires a relatively very high processing temperature.
FIG. 2 illustrates a schematic sectional view for showing an example of silicon direct bonding. As shown in the FIG. 2, silicon direct bonding for initial bonding is performed by heating upper and lower silicon substrates 10, 10′ to a very high temperature to form a silicon oxide film thereon and to be bonded. Basically, silicon direct bonding requires surface treatment of a wafer and a very high processing temperature so that a silicon oxide film may be formed on the interface. Therefore, the bonding yield in silicon direct bonding is also affected by particles, and is more greatly affected by the surface roughness of the wafer than is anodic bonding.
FIG. 3 illustrates a schematic sectional view to for showing an example of eutectic bonding. As shown in the FIG. 3, the bonding is performed by forming eutectic material 11, 11′ on respective contact surfaces of upper and lower substrates 10, 10′, and applying a pressure at a eutectic temperature or higher to effect the bonding. The bonding is achieved by forming a secondary film by a reaction occurring when the respective interfaces come into contact. Therefore, the surface state of the two wafers is of considerable importance.
In addition, as shown in FIG. 4, a temperature required to effect a phase transition from a solid state to a liquid state varies depending on rations of elements involved. FIG. 4 is a graphical representation to illustrate the eutectic characterization curve of Au—Si. In the case that the ratio of the atomic weight of Si is about 18%, Au and Si can be phase-transitioned to a liquid state by mutual interaction at a temperature of about 363° C. This phase-transition temperature is much lower than the respective melting point of either element, but the phase-transition temperature may change greatly if the ratio of elements changes. Therefore, the bonding is extremely sensitive to the ratio control of atomic weight.
FIG. 5 illustrates a sectional view for showing adhesive bonding using an adhesive. As shown in FIG. 5, the bonding is performed by coating an adhesive 12 on a substrate 10′, applying pressure and heating. In this case, solid state bonding is achieved by vaporizing a solvent inside the adhesive 12 during the bonding. Bonding methods that may be used include epoxy bonding, glass-frit bonding, solder paste bonding and the like.
However, a bonding layer comprised of the adhesive 12 is generally formed by screen printing or dispensing, making it difficult to control the shape of the adhesive, and resulting in a greatly increased pattern size. The roughness of a wafer created during the manufacturing of the MEMS device may be recovered, but the great increase in size of the bonding layer by the pressure causes a disadvantage. In addition, discharged gas that is generated by the solvent in the bonding material has an adverse affect on the MEMS device.
Meanwhile, FIG. 6 illustrates a sectional view for showing a conventional method used to create an electrical interconnection through a via hole 13 in a conventional MEMS device package. As shown in FIG. 6, with the presence of several micrometers of an under-cut 13a formed during the formation of the via hole 13, electrically connecting an electrode 14 of a lower substrate 10 with circuits 15 of external terminals is a difficult problem.